New principles of material selection for lithium-sulfur batts

• U.S. Argonne National Laboratory researchers have tested a group of electrolytes which are supposed to maximize the Li-S batts performance. The team has established a selection approach to help choosing the best electrolyte for a certain battery cell.

Li-S batteries are among storage units considered to be able to provide a much higher capacity potential compared to Li-ion batts, at the same time utilizing affordable and widespread materials. 

However, Li-S performance is worsened by undesired reaction called ‘polysulfide shuttling’. The latter means that in the process of charging, the partially oxidated Li-S compounds sometimes get dissolved into the electrolyte. The chemicals get reduced on anodes while getting oxidized at cathodes, which results in worse battery charging. 

Such a chemical reaction takes place due to polysulfide dissolvability in normal electrolyte consisting of dioxolanes and dimethoxyethanes. But today we have a new type of electrolytes – hydrofluoroethers. Such media are less suitable for polysulfide dissolution. 

No magic wand 

The research team has compared characteristics of different HFEs. The researchers have managed to determine interdependence between chemical composition and the electrochemical properties of the substance. As a result, they have made a new rule to forecast the hydrofluoroether solubility and conductivity levels. 

The scientists state that their experiment provides useful understanding of PS shuttle mechanism and is likely to help choose optimal hydrofluoroether for a definite storage unit. 

When testing properties of various materials, the researchers have concluded that electrolytes least disposed to PS shuttling at the same time appear the worst conductors, which means new researches in an attempt to improve the available materials are still ahead.